1. Field of the Invention
The present invention relates to a linear displacement device and, more specifically, to a roller nut assembly for use with a lead screw of a linear displacement device.
2. Discussion
Linear displacement devices are generally known in the art. Linear displacement devices are used for the rapid, smooth and precise adjustment of linear mechanisms, such as zoom lenses, micrometers, and stepper motor stages, by automatic screw-turning or nut-turning means.
The standard linear displacement device utilizes a lead screw and a standard nut for converting the rotary motion of the lead screw element to relative linear displacement of the nut. The lead screws are generally driven by a stepper motor which causes the lead screw to rotate in increments which causes a corresponding incremental linear movement of the nut.
For proper operation of the conventional lead screw and nut assembly, the nut must be preloaded and periodically reset to produce a repeatable performance. The preload between the nut and the spindle has to be extremely high in order for the linear displacement device to be play-free. The extremely high preload which is required greatly contributes to the amount of friction between the mating surfaces between the lead screw and nut in the linear displacement device. In a typical linear displacement device, thirty to forty percent of the motor torque is used just to overcome the friction between the static nut and the rotating lead screw.
Additionally, if the linear displacement device is used in a vertical orientation, the lubricant between the lead screw and the standard nut will migrate and leave dry the preloaded mating surfaces of the lead screw and nut, thus increasing friction even further, and contributing to the failure of these units.
Accordingly, it is desirable in the art of linear displacement devices to provide a linear displacement device which greatly decreases the amount of friction between the rotating lead screw and the linear displacing nut.